Variations and Early Selections of Growth Traits in Maternal Clones and Open-Pollinated Progeny Families from the Same Plus Trees of Tilia mandshurica

Tilia mandshurica is a multi-purpose tree species with high values for timber production, landscape ornamentation, and nectar yield. Growth traits serve as core evaluation indices for its genetic improvement, and clarifying the maternity–progeny genetic relationship is essential for efficient selective breeding. In this study, 66 maternal clones and their corresponding open-pollinated progeny families derived from the same plus trees were used as experimental materials. Six key growth traits, including tree height, basal diameter, clear bole height, branch angle, crown width, and stem straightness, were systematically measured and analyzed. Extremely significant variances in all investigated growth traits were observed among both maternal clones and progeny families. For maternal clones, the phenotypic coefficient of variation, genotypic coefficient of variation, and repeatability ranged from 37.3% to 77.2%, 1.0% to 29.1%, and 0.4286 to 0.6587, respectively. For progeny families, the phenotypic coefficient of variation and genotypic coefficient of variation varied from 35.4% to 66.9% and 0.7% to 26.7%, with heritability ranging from 0.3671 to 0.6255. Significant phenotypic and genetic correlations for growth traits were detected between maternal clones and progeny families, excluding stem straightness. Integrated principal component analysis and multi-trait comprehensive evaluation screened eight elite maternal clones (LJ03, LJ19, LJ21, LJ32, LJ40, LJ47, LJ52, LJ63) and ten elite progeny families (LJ03, LJ09, LJ21, LJ27, LJ32, LJ40, LJ46, LJ47, LJ52, LJ63). Among these materials, seven germplasms (LJ03, LJ21, LJ32, LJ40, LJ47, LJ52, LJ63) exhibited excellent performance in both clonal and family populations. The elite clones yielded genetic gains of 4.4–26.2% and realistic gains of 10.3–42.4%, while the elite families presented genetic gains of 1.5–21.2% and realistic gains of 3.1–33.8%. This study clarifies the genetic variation and maternity –progeny genetic linkage of growth traits in T. mandshurica, provides excellent elite germplasm resources for genetic improvement, and offers a theoretical and practical basis for the future construction of high-quality seed orchards of this species.